Stannous ions, in particular stannous salts such as stannous fluoride, are known anti-microbial agents that are used in dentifrices as agents for preventing plaque. However, some disadvantages of stannous salts include instability, tendency to stain teeth, astringency and unpleasant taste for users.
Zinc ions, in particular zinc salts, are also known anti-microbial agents that are sometimes incorporated into dentifrice formulations. Use of various zinc salts often is limited by the solubility of the zinc, undesirable consumer astringency when higher levels of zinc are utilized, and the reactivity of the zinc once zinc ions are available for reaction (i.e., the zinc ions sometimes cause adverse reactions within the formulation).
Polyphosphates and ionic active ingredients have been used in dentifrices to promote oral health. Polyphosphates are known anti-tartar agents that help retard calculus formation.
While such ingredients have previously been used in dentifrices, for several reasons it has proven challenging to provide these ingredients together in a formulation having satisfactory chemical and physical stability.
One attempt to provide stable dentifrice compositions is to reduce the amount of water present in the composition. However, as described in the background of U.S. Patent Application Publication 2012-0207686 reducing the level of water, and optionally replacing some or all of the removed water with a humectant, creates problems in obtaining acceptable rheology and thickening properties in the composition.
When water, which is a highly polar solvent, is removed, some conventional thickening agents tend to inadequately gel up. Attempts to reduce water content in dentifrice compositions have included the dentifrices described in, e.g., EP 0 638 307 B1; U.S. Pat. No. 4,647,451; and U.S. Pat. No. 5,670,137. Such known formulations have been shown to exhibit progressive thickening over time, which prolongs the time period or even prevents the dentifrice from reaching a rheological steady state. Ideally, dentifrice formulations need to reach a steady state for consumer acceptance within two weeks. If a formulation routinely increases in viscosity over time, dispensing of the formulation will become difficult, which will likely result in consumer dissatisfaction.
US Patent Application Publication 2012/0207686 A1 discloses dentrifices that may contain stannous ions, zinc ions, and certain polyphosphates that comprise, in a single phase, an orally acceptable vehicle, the vehicle including a thickening agent comprising a polymer system comprising, in combination, a cross-linked polyvinylpyrrolidone and a gum, wherein the dentifrice composition has a total water content of less than 10% based on the weight of the composition.
There is a need in the art to provide low water single phase dentifrice compositions that have an improved rheological profile, and in particular have a stable rheology of adequate viscosity that effectively reduces or eliminates progressive thickening of the composition over time which in turn provides a composition that can effectively be dispensed over the period of its shelf life.